Utilization of alunite ore in the process of making superphosphates



UETE ITS ENE" HQ.

ALEXANDER MATHESON. OF LONDON, ENGLAND.

UTILIZATION OF ALUNITE ORE IN THE PROCESS OF MAKING SUPERPHOSPHATES.

No Drawing.

perphosphates, of which the following is a specificatlon This inventionrelates to the utilization of alunite ore for the purpose of makingsuperphosphates and fertilizers.

A typical analysis of alunite is as follows Potash (K 0) 7.70 percent.

Alumina (A1 0 34.20

Sulphuric anhydride (SO L 38.50 Silica (SiO 16.40 Ferric ()xide (Fe O1.00 Water (H O) 2.20

All the known deposit of alunite'contain from a minimum of 18 up to 38per cent of sulphuric acid, and from a minimum of 4 up to 10 per cent ofpotash.

When alunite is roasted, or calcined, a proportion of the sulphuric acid(about 27 per cent of the S0 present) combines with the potassium,forming sulphate of potassium (K S0 and the rest is driven off in theform of sulphuric anhydride (S9 sulphur dioxide (S0 and oxygen (0), inproportions varying according to the temperature of the furnace.

Accordin to this invention the alunite is roasted,'in t e absence ofmaterial quantities of air, at a temperature of about 700 C. to 900 C.and the mixture of sulphur gases is caused in the presence of suflicientwater to form sulphuric acid to act on bones or minerals containingphosphate. The phosphates in the material so treated are in this mannerconverted very economically into the superphosphates, forming a valuablechemical manure or fertilizer.

The superphosphates may be prepared in v the following manner I mayenclose alunlte which has already.

been broken into cubes and calcined (and which preferably but notnecessarily has been ground up to pass through a 40 mesh screen), alongwith phosphates also ground, in a retort tower or other suitablecontainer,

1 mixed together in the proportion required,

having regard to the content in potash of Specification of LettersPatent.

the mixed fertilizer to be produced.

Patented Apr. 1%. i022.

Application filed. August 19, 1920. Serial No. 404,654.

phosphate of lime desired to be contained in The sulphur gases evolvedfrom alunite in the process of calcination in a closed furnacepreferably one such as is hereinafter described, are then passed intoand through the mixed phosphates and calcined alunite along with a sprayof water or a 'et of steam so regulated as to produce H 0 as beforedescribed until the mixture. while being turned over or otherwiseagitated, becomes fully saturated with sulphuric acid.

Preferably the alunite, broken into cubes having faces of about one inchsquare, is calcined in an externally heated, muffled and mechanicallyrabbled furnace having hearths situated one above another, so arrangedthat the broken alunite is charged on the top hearth and continuouslypassed downwards from hearth to hearth to the lowest hearth from whichit is finally discharged. Only the lowest hearth or the lower hearths isor are externally heated to a temperature of from 700 C. to 900 (7. orthereabouts, and the S0 S0 and (l evolved from the alunite in passing upover the other hearths gradually dry and heat the alunite thereon as thelatter passes down to the ilowest hearths and highest furnace heat. TheS0,

and O re-combine to form SQ, as the gradually'cooling gases come intocontact with the iron oxide contained in "the alunite on the upperhearths. At the same time, the ascending gases become gradually cooledso that on leaving the top of the furnace they are at a temperatureconvenient for further treatment or use. The furnace should be of suchheight and contain such a number of hearths as will effect the requireddegree of cooling of the ascending gases. In using these gases for themanufacture of superphosphates, I lead them direct into a closed retorttower or other suitable container, charged with phosphates until therequisite amount of SO, has been absorbed by the phosphates as indicatedby test sampling.

' The cooled gases are passed into the retort or tower along with aspray of water so regulated as to produce sulphuric acid. Any sulphurousacid (H SOQ formed as the result of the incomplete recombination of theS0 and O in the upper portion of the furnace is readily oxidized tosulphuric acid in presence of the traces of iron compounds.

usually existing insufficient calcium superphosphate commences to breakup into tricalcium phosphate and phosphoric acid. On cooling and storingreversal of the reaction takes place, the flricalcium phosphate andphosphoric acid reacting to give the desired superphosphates. A certainamount of potassium phosphate, varyin with the conditions, may be alsoformed, en ancing the value of the product as a fertilizer. In fixingthe proportion of alunite to phosphates in each charge, regard must behad to the amount of S0, available from the alunite and that required bythe phosphates used, and also to the respective amounts of phosphoricacid and potassium required in the mixed fertilizer to be produced. Thetreated phosphates are stored in a'bin or in open dumps under sheds, inthe usual manner, in order steam. The question ofwhether any added wateris required and if so what amount will depend upon the constituents ofthe alunite used and the moisture originally present.

What I claim and desire to secure by Letters Patent of the United Statesis 1. A process for producing superphosphates, which consists inroasting alunite in a furnace in the absence of material quanti'ties ofair to a temperature of about 700 C. to 900,C., withdrawing the sulphurgases emitted from the alunite from the furnace and passing the saidgases through phosphate containing materials in the pres ence ofsufficient water to form sulphuric acid from the gases.

2. A process for producing superphos- 'phates. which consists insubjecting alunite,

in its passage through a furnace, to progressively increasing heat, inthe absence of material quantities of air, to drive off its-sulphurgases, passing said gases through the alunite in a direction opposite tothatin which the alunite moves, drawing ofi the gases at the end oftheir travel through the alunite, and then passing the gases throughphosphate containing materials in the presence of sufficient water toform sulphuric acid from the said gases.

ALEXANDER MATHESON.

